In 1965 a tumor associated antigen was found (J. Exptl. Med. 121 439-462, 1965) which was subsequently designated as carcinoembryonic antigen (hereinafter CEA). CEA circulates and may be detected in human blood--serum or plasma--by a radioimmunoassay. However it does not appear to be associated with breast cancer.
We have now suceeded in locating, isolating and purifying a series of antigens which are associated with breast cancer tumors. These were initially designated "MK" and "fractionated MK" but we have now designated them BCA-Breast Cancer Antigens. "MK" and "fractionated MK" may be regarded as crude and pure forms of BCA respectively.